Method of fabricating a light emitting device having a stacked structure

ABSTRACT

A method of fabricating a light emitting device includes (i) determining whether each measurement location is defective or not based on a measurement result of the emission wavelength of each location, (ii) forming a test stacked structure by combining one of the first wafers, one of the second wafers, and one of the third wafers in a set of wafers, and (iii) calculating a combination yield of the test stacked structure based on a count of defective measurement locations that overlap in the test stacked structure.

CROSS-REFERENCE OF RELATED APPLICATIONS AND PRIORITY

The Present Application is a Non-provisional Application which claimsthe benefit of the filing date of U.S. Provisional Application Ser. No.62/987,132 filed Mar. 9, 2020, the disclosure of which is incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a method of fabricating a lightemitting device, and in particular, to a method of fabricating a lightemitting device having a stacked structure.

BACKGROUND

As an inorganic light source, light emitting diodes have been used invarious fields including displays, vehicular lamps, general lighting,and the like. With various advantages such as long lifespan, low powerconsumption, and rapid response, light emitting diodes have beenreplacing existing light sources in the art.

Light emitting diodes have been used as backlight light sources indisplay apparatuses. However, LED displays that directly realize imagesusing the light emitting diodes have been recently developed.

In general, a display apparatus realizes various colors through mixtureof blue, green and red light. In order to realize various images, thedisplay apparatus includes a plurality of pixels, each of which hassubpixels corresponding to blue, green and red light, respectively. Acolor of a certain pixel is determined based on the colors of thesub-pixels so that images can be realized through combination of suchpixels.

Since LEDs can emit various colors depending upon materials thereof, itis possible to provide a display apparatus by arranging individual LEDchips emitting blue, green and red light on a two-dimensional plane.However, when one LED chip is arranged in each sub-pixel, the number ofLED chips may increase, which may require excessive time for a mountingprocess during fabrication.

Recently, in order to solve disadvantages of a conventional LED displayin which subpixels are arranged on a two-dimensional plane, a lightemitting device having a stacked structure in which subpixels of variouscolors are stacked in the vertical direction has been developed. Thelight emitting device having a stacked structure is fabricated bystacking a plurality of wafers for implementing light of differentcolors.

FIG. 1 is a schematic perspective view illustrating a method offabricating a light emitting device having a stacked structure accordingto the related art.

Referring to FIG. 1 , a first wafer 210, a second wafer 310, and a thirdwafer 410 are prepared. The first wafer 210 includes a first substrate21 and a first LED stack 23, the second wafer 310 includes a secondsubstrate 31 and a second LED stack 33, and the third wafer 410 includesa third substrate 41 and a third LED stack 43.

Thereafter, the first wafer 210, the second wafer 310, and the thirdwafer 410 are stacked to fabricate a light emitting device. Accordingly,the light emitting device has a structure in which the first LED stack21, the second LED stack 33, and the third LED stack 43 are stacked.

Meanwhile, since the first, second, and third wafers 210, 310, and 410are stacked on one another to fabricate the light emitting device, thelight emitting devices fabricated by stacking the first, the second andthe third wafers 210, 310, and 410 have a lower yield than that of eachof the wafers 210, 310, and 410. In particular, as illustrated in FIG. 1, since defective locations 23 f, 33 f, and 43 f in the wafers 210, 310,and 410 are different from one another, the light emitting devicesfabricated by stacking these wafers has a considerably low yield.Accordingly, due to the defective location of one wafer, the lightemitting device including favorable locations of the other wafers isdiscarded, resulting in a large loss.

SUMMARY

Exemplary embodiments provide a method of fabricating a light emittingdevice having a stacked structure for increasing a process yield of thefabrication.

In one or more embodiments according to the teachings of the presentdisclosure, a method of fabricating a light emitting device having astacked structure is provided. The method includes (i) measuring anemission wavelength for each predetermined measurement location of eachwafer in a first group of wafers. The first group of wafers includes aplurality of first wafers, a plurality of second wafers, and a pluralityof third wafers, and a set of wafers comprises at least one of the firstwafers, at least one of the second wafers, and at least one of the thirdwafers. The method further includes (ii) determining whether eachmeasurement location is defective or not based on a measurement resultof the emission wavelength of each location, (iii) forming a teststacked structure by combining said one of the first wafers, said one ofthe second wafers, and said one of the third wafers in the set ofwafers, (iv) calculating a combination yield of the test stackedstructure based on a count of defective measurement locations thatoverlap in the test stacked structure, (v) selecting one or moreresultant combinations of the first, the second and the third wafers bycomparing each combination yield of the test stacked structure, and (vi)performing a subsequent process using the resultant combinations of thefirst, the second and the third wafers. The subsequent process includesforming a final stacked structure with the selected resultantcombinations of first, the second and the third wafers.

In at least one variant, the method further includes performing thesubsequent process on the combinations of first, the second and thethird wafers, where each combination has a combination yield greaterthan or equal to a reference value.

In another variant, the method further includes determining each yieldof each wafer in the first group based on the measurement result of theemission wavelength of each location.

In another variant, determining whether each location is defective ornot further includes determining whether or not the measurement resultof the emission wavelength of each location is in a preset range from atarget wavelength. Measuring the emission wavelength further comprisesmeasuring the emission wavelength using photoluminescence.

In another variant, the method further includes sorting the plurality offirst wafers to follow a selected order. Forming the test stackedstructure further includes forming the test stacked structure bycombining each first wafer following the sorted order with each secondwafer and each third wafer selected in random order, respectively.

In at least one variant, the method further includes preparing the firstgroup of wafers including a total of n first wafers, a total of m secondwafers, and a total of k third wafers. Here, n, m and k are naturalnumbers greater than zero. Where m and k are equal to n, forming thetest stacked structure further includes forming the test stackedstructure that include (n!)² different combinations of the first wafers,the second wafers, and the third wafers. Calculating the combinationyield of the test stacked structure further includes calculating thecombination yield of all or a part of the (n!)² different combinationsbased on the count of defective measurement locations that overlap ineach test stacked structure.

In another variant, selecting the resultant combinations furthercomprises comparing the combination yield for all or a part of the (n!)²different combinations of the first wafers, the second wafers, and thethird wafers.

In further another variant, the method further comprises calculatingtotal combination yield Yt by summing the combination yield of all of apart of the (n!)² different combinations of the first wafers, the secondwafers, and the third wafers.

In another variant, selecting the resultant combinations furthercomprises selecting the resultant combinations of the first, the secondand the third wafers in the order of a highest combination yield.

In further another variant, where m is greater than n, selecting the setof wafers from the first group of wafers further comprises selecting nsets of wafers from the first group of wafers, calculating thecombination yield of the test stacked structure based on the n sets ofwafers, selecting (m−n) sets of wafers from the first group of wafers,and calculating the combination yield of the test stacked structurebased on the (m−n) sets of wafers.

In another variant, the method further includes preparing a second groupof wafers including wafers of identical types to types of the firstgroup of wafers, measuring the emission wavelength for eachpredetermined measurement location of each wafer in the second group,forming another test stacked structure by combining a portion of thewafers in the first group and the wafers in the second group, andcalculating combination yields of another test stacked structure basedon a count of defective measurement locations that overlap in anothertest stacked structure.

In one or more embodiments according to the teachings of the presentdisclosure, a computer-readable storage medium, storing a computationalprogram for calculating combination yields of first wafers, secondwafers, and third wafers in a first group, on the basis of the data onwhether locations on each wafer in the first group of wafers including agroup of first wafers, a group of second wafers, and a group of thirdwafers is defective or not, respectively. The computational program,upon execution by a processor, is configured to perform operations,comprising determining whether or not a measurement result of anemission wavelength for each predetermined measurement location of eachwafer is in a preset range from a target wavelength, upon determinationthat the measurement result is outside of the preset range from thetarget wavelength, determining that a corresponding measurement locationto the measurement result has a defect, and calculating a combinationyield of a test stacked structure based on a count of overlappingdefective measurement locations in the test stacked structure. The teststacked structure includes a first wafer, a second wafer, and a thirdwafer, selected from each group and combined in each differentpredetermined order. The operation further includes determining aresultant combination of the first wafer, the second wafer and the thirdwafer by comparing each combination yield of each test stackedstructure.

In at least one variant, the operations further comprise determiningeach yield of each wafer in the first group based on presence or absenceof the defect on each wafer.

In another variant, the group of first wafers comprises a total n offirst wafers; the group of second wafers comprises a total m of secondwafers; and the group of third wafers comprises a total k of thirdwafers, where n, m, and k are natural numbers and greater than zero.Where n, m, and k are an identical number, the operations furtherinclude calculating the combination yield of the test stacked structurethat include (n!)² different combinations of the first wafers, thesecond wafers, and the third wafers.

In one or more embodiments according to the teachings of the presentdisclosure, a method of fabricating a light emitting device having astacked structure according to an exemplary embodiment includes (i)preparing a first group of wafers including at least two types ofwafers, (ii) measuring an emission wavelength for each location of eachwafer in the first group, (iii) calculating combination yields of thewafers in the first group based on the measurement result, (iv)determining combinations of wafers based on the combination yields, and(v) performing a subsequent process using the determined combinations ofwafers.

In another embodiment, a computer-readable storage medium stores acomputational program for calculating combination yields of firstwafers, second wafers, and third wafers in a first group, on the basisof the data on whether locations on each wafer in the first group ofwafers including a group of first wafers, a group of second wafers, anda group of third wafers are defective or not, respectively.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view illustrating a method offabricating a light emitting device having a stacked structure accordingto the related art.

FIG. 2 is a schematic flowchart illustrating a method of fabricating alight emitting device having a stacked structure according to one ormore embodiments of the present disclosure.

FIG. 3 is a schematic plan view illustrating a mapping process of afirst wafer.

FIG. 4 is a schematic plan view illustrating a mapping process of asecond wafer.

FIG. 5 is a schematic plan view illustrating a mapping process of athird wafer.

FIG. 6A is a table for showing one example of combination yieldsaccording to combinations of wafers.

FIG. 6B is a table for showing another example of combination yieldsaccording to combinations of wafers.

FIG. 7 is a schematic perspective view illustrating a method offabricating a light emitting device having a stacked structure accordingto one or more embodiments of the present disclosure.

FIG. 8 is a schematic flowchart illustrating a method of fabricating alight emitting device having a stacked structure according to one ormore embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. The following embodiments are provided by wayof example so as to fully convey the spirit of the present disclosure tothose skilled in the art to which the present disclosure pertains.Accordingly, the present disclosure is not limited to the embodimentsdisclosed herein and can also be implemented in different forms. In thedrawings, widths, lengths, thicknesses, and the like of devices can beexaggerated for clarity and descriptive purposes. When an element orlayer is referred to as being “disposed above” or “disposed on” anotherelement or layer, it can be directly “disposed above” or “disposed on”the other element or layer or intervening devices or layers can bepresent. Throughout the specification, like reference numerals denotelike devices having the same or similar functions.

In one or more embodiments according to the teachings of the presentdisclosure, a method of fabricating a light emitting device includes (i)determining whether each measurement location is defective or not basedon a measurement result of the emission wavelength of each location,(ii) forming a test stacked structure by combining one of the firstwafers, one of the second wafers, and one of the third wafers in a setof wafers, and (iii) calculating a combination yield of the test stackedstructure based on a count of defective measurement locations thatoverlap in the test stacked structure

In one or more embodiments according to the teachings of the presentdisclosure, a method of fabricating a light emitting device having astacked structure includes preparing a first group of wafers includingat least two types of wafers, measuring an emission wavelength for eachlocation of each wafer in the first group, calculating combinationyields of the wafers in the first group based on the measurement result,determining combinations of wafers based on the combination yields, andperforming a subsequent process using the determined combinations ofwafers.

Before performing the process, an optimum combination may be derived bypre-calculating combination yields of a plurality of wafers, and thus, ayield of fabricating a light emitting device may be improved.

In at least one variant, the first group of wafers may include firstwafers each having a first substrate and a first LED stack grown on thefirst substrate, second wafers each having a second substrate and asecond LED stack grown on the second substrate, and third wafers eachhaving a third substrate and a third LED stack grown on the thirdsubstrate. The first, second, and third LED stacks may be configured toemit light of different colors from one another.

In another variant, the first LED stack may be configured to emit redlight, the second LED stack may be configured to emit blue light, thethird LED stack may be configured to emit green light, and the secondLED stack may be disposed between the first LED stack and the third LEDstack.

In further another variant, the first LED stack may be configured toemit red light, the second LED stack may be configured to emit greenlight, the third LED stack may be configured to emit blue light, and thesecond LED stack may be disposed between the first LED stack and thethird LED stack.

In further another variant, calculating the combination yields of thefirst group of wafers may include calculating total combination yieldsYt according to all combinations of the wafers in the first group, anddetermining combinations of wafers based on the combination yields maybe determined with a maximum combination yield among the totalcombination yields.

In another variant, calculating combination yields of the first group ofwafers may include fixing an order of one type of wafers in advance, andcombination yields with other types of wafers may be calculated in theorder of one type of wafers.

In further another variant, determining combinations of wafers based onthe combination yields may be determined in order of high combinationyield with other types of wafers in the order of one type of wafers.

In some forms, the subsequent process may be performed for allcombinations of wafers. In other forms, the subsequent process may beperformed on combinations each having a combination yield greater thanor equal to a reference value among all combinations of wafers.

In one form, the reference value may be about 50%, about 60%, or about70%.

In one or more embodiments according to the teachings of the presentdisclosure, the method of fabricating the light emitting device mayinclude preparing a second group of wafers including wafers of identicaltypes as those of the first group of wafers, measuring an emissionwavelength for each location of each wafer in the second group,calculating combination yields of a portion of wafers in the first groupand the wafers in the second group based on the measurement result,determining combinations of wafers based on the combination yields, andperforming a subsequent process on the portion of wafers in the firstgroup and the wafers in the second group using the determinedcombinations of wafers.

In at least one variant, the subsequent process may be performed oncombinations each having a combination yield greater than or equal to areference value among all combinations of wafers.

The portion of wafers in the first group may be at least a portion ofwafers having combination yields less than the reference value among thecombinations of the first group of wafers.

Calculating combination yields of the wafers in the first group may beperformed using a computational program.

The computational program may be stored in a computer-readable recordingmedium.

In another variant, a yield of each wafer may be calculated bydetermining whether each location is defective or not from themeasurement result of an emission wavelength of each location.Furthermore, whether each location is defective or not may be determinedin a preset range from a target wavelength.

The emission wavelength may be measured using photoluminescence.

In one or more embodiments according to the teachings of the presentdisclosure, a computer-readable storage medium stores a computationalprogram for calculating combination yields of first wafers, secondwafers, and third wafers in a first group, on the basis of the data onwhether locations on each wafer in the first group of wafers including agroup of first wafers, a group of second wafers, and a group of thirdwafers are defective or not, respectively.

In at least one variant, the computational program may calculatecombination yields for all combinations of the first wafers, the secondwafers, and the third wafers.

In another variant, the computational program may fix an order of anyone of the first wafers, the second wafers, and the third wafers, andcombination yields of the first wafers, the second wafers, and the thirdwafers may be calculated according to the fixed order of the wafers.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings.

FIG. 2 is a schematic flowchart illustrating a method of fabricating alight emitting device having a stacked structure according to one ormore embodiments, and FIGS. 3 through 5 are schematic plan viewsillustrating a mapping process of first, second, and third wafers,respectively, and FIGS. 6A and 6B are tables for showing yieldsaccording to combinations of wafers.

(Step 101)

Referring to FIG. 2 , first, in Step 101, a first group of wafers isprepared. The first group of wafers may include, for example, aplurality of first wafers, a plurality of second wafers, and a pluralityof third wafers. A first wafer 210 is shown in FIG. 3 , a second wafer310 is shown in FIG. 4 , and a third wafer 410 is shown in FIG. 5 .Although only one first wafer R1, only one second wafer B1, and only onethird wafer G1 are shown in FIGS. 3, 4, and 5 , respectively, there willbe provided a plurality of first wafers, a plurality of second wafers,and a plurality of third wafers. By way of example, there may be twelve(12) first wafers, twelve (12) second wafers and twelve (12) thirdwafers, a total of thirty six (36) wafers. A plurality of first wafers210, a plurality of second wafers 310, and a plurality of third wafers410 may be prepared and designated as the first group. Using the aboveexample, the first group may include a total of thirty six (36) wafers.Herein, although the first group is described as including three typesof wafers by way of example, the inventive concepts are not limited tothree types thereof. For example, the first group may include two typesof wafers, or may include four or more types of wafers.

The number of each of the first, second, and third wafers 210, 310, and410 included in the first group may be identical to one another, but itis not limited thereto and may be different from one another. Forexample, the plurality of first wafers 210 may be wafers on which agrowth process has been performed together in one growth apparatus.These wafers are provided through an identical run. Similarly, theplurality of second wafers 310 may also be wafers on which a growthprocess has been performed together in one growth apparatus, and theplurality of third wafers 410 may also be wafers on which a growthprocess has been performed together in one growth apparatus. However,the inventive concepts are not limited thereto. For example, the firstgroup includes the first wafers 210, the second wafers 310, or the thirdwafers 410 grown multiple times in one growth apparatus or grown inmultiple growth apparatuses. That is, the first group of wafers may beprovided through multiple runs by the same or different growthapparatuses. For convenience of description, it will be described thattwelve (12) first wafers 210, twelve (12) second wafers 310, and twelve(12) third wafers 410 are included in the first group, in the followingexemplary embodiment. However, as described above, the number of wafersincluded in the first group is not limited thereto, and may be smalleror greater than 12.

Meanwhile, each of the first wafers 210 includes a first LED stack 23grown on a first substrate 21, each of the second wafers 310 includes asecond LED stack 33 grown on a second substrate 31, and each of thethird wafers 410 includes a third LED stack 43 grown on a thirdsubstrate 41.

FIG. 3 is a schematic plan view illustrating a mapping process of afirst wafer. FIG. 4 is a schematic plan view illustrating a mappingprocess of a second wafer. FIG. 5 is a schematic plan view illustratinga mapping process of a third wafer.

The first LED stack 23 may emit light of a longer wavelength than thoseof light emitted from the second and third LED stacks 33 and 43, and thesecond LED stack 33 may emit light of a longer wavelength than that oflight emitted from the third LED stack 43. For example, the first LEDstack 23 may be an inorganic light emitting diode emitting red light,the second LED stack 33 may be an inorganic light emitting diodeemitting green light, and the third LED stack 43 may be an inorganiclight emitting diode emitting blue light.

In another exemplary embodiment, to adjust a color mixing ratio of lightemitted from the first, second, and third LED stacks 23, 33, and 43, thesecond LED stack 33 may emit light of a shorter wavelength than that oflight emitted from the third LED stack 43. Accordingly, luminousintensity of light emitted from the second LED stack 33 may be reducedand luminous intensity of light emitted from the third LED stack 43 maybe increased. For example, the first LED stack 23 may be configured toemit red light, the second LED stack 33 may be configured to emit bluelight, and the third LED stack 43 may be configured to emit green light.

Hereinafter, although it is exemplarily described that the second LEDstack 33 emits light of a shorter wavelength than that of light emittedfrom the third LED stack 43, for example, blue light, but it should benoted that the second LED stack 33 may emit light of a longer wavelengththan that of light emitted from the third LED stack 43, for example,green light.

Each of the first, second, and third LED stacks 23, 33, and 43 mayinclude an n-type semiconductor layer, a p-type semiconductor layer, anda well layer. The first LED stack 23 may include an AlGaInP-based welllayer, the second LED stack 33 may include an AlGaInN-based well layer,and the third LED stack 43 may include an AlGaInP-based or AlGaInN-basedwell layers.

(Step 201)

In Step 201, a performance measurement is carried out for each wafer inthe first group. The performance measurement for locations in each waferis carried out, and whether each location is defective or not may bedetermined using the measured value. For example, as illustrated in FIG.3 , it is checked whether each of regions 23 m of the first LED stack 23grown on the first wafer 210 is defective or not. The result of checkingwhether each location is defective or not may be stored and mapped sothat it can be checked visually by a user. In some forms, the mappeddata can be displayed on a screen or printed on a tangible medium andcan be visually inspected by a user. A user may see displays of thewafers 210(R1), 310(B1), and/or 410(G1) on the screen as illustrated inFIGS. 3-5 and defective regions 23 m may be distinctly displayed. Asillustrated in FIGS. 4 and 5 , the same performance measurement andmapping for each of regions 33 m and 43 m may be carried out for thesecond wafer 310 and the third wafer 410.

An area for each location, such as the regions 22 m, 33 m, and 43 mshown in FIGS. 3-5 , for determining whether there is a defect or notmay be arbitrarily set, and performance of a measuring tool may beconsidered. For example, a light emission wavelength at each location ismeasured using PL (photoluminescence), through which whether eachlocation is defective or not may be determined. In this case, a size ofthe measurement location may be determined by a PL beam size. Inaddition, it is determined whether there are defects at every locationon the first wafer 210 where light emitting devices are to befabricated, by measuring the emission wavelengths for predeterminedlocations.

It is possible to determine whether each location is defective or not,by pre-determining a favorable wavelength range. For example, when theemission wavelength measured using the PL is out of a certain range froma target wavelength, it may be determined as defective. A certain rangemay be set to be, for example, 2 nm or the like, or may be set to be aratio of 1% or 0.5% of the target wavelength.

In Step 201, the performance measurement of all the wafers in the firstgroup is completed, and whether each location of each wafer is defectiveor not is determined. According to the above results, a yield of eachwafer may also be extracted.

(Step 301)

In Step 301, combination yields of the first group of wafers arecalculated. The combination yields of the wafers may provide differentand more information than an individual yield of each wafer. As thefirst, the second, and the third wafers 210, 310, and 410 are stacked onone another to fabricate the light emitting device, the light emittingdevices fabricated by stacking the first, the second and the thirdwafers 210, 310, and 410 may have a lower yield than that of each of thewafers 210, 310, and 410 in some instances. As previously described inconnection with FIG. 1 , since defective locations 23 f, 33 f, and 43 fin the wafers 210, 310, and 410 may be different from one another, thelight emitting devices fabricated by stacking these wafers may have aconsiderably low yield.

The method of fabricating a light emitting device according to theteachings of the present disclosure includes forming a test stackedstructure by combining one of the first wafers 210, one of the secondwafers 310, and one of the third wafers 410 such that a combinationyield of the test stacked structure is calculated based on a count ofdefective measurement locations that overlap in the test stackedstructure. Each combination yield of each test stacked structure will becompared and one or more resultant combinations of the first, the secondand the third wafers 210, 310, and 410 will be selected. A final stackedstructure can be fabricated with the resultant combinations that providehigher yields.

There are various manners in which the combination yields arecalculated. In an exemplary embodiment, all possible cases ofcombinations may be considered, as will be described below. Moreparticularly, a yield of each combination may be calculated through allpossible combinations of the first, second, and third wafers 210, 310,and 410 in the first group, through which total combination yields maybe derived. For the combinations of wafers in the first group, aplurality of total combination yields may be derived, and combinationsof wafers providing a maximum combination yield may be identified amongthe total combination yields. This will be described in detail withreference to FIGS. 6A and 6B.

FIGS. 6A and 6B are tables for showing yields according to combinationsof wafers. Herein, the first, second, and third wafers 210, 310, and 410included in the first group are grouped as R group (RG; R1 through R12),B group (BG; B1 through B12, and G group (GG; G1 through G12),respectively. Herein, each of the R group, B group, and G group includes12 wafers, and R1 through R12, B1 through B12, and G1 through G12represent respective wafers, but as described above, the inventiveconcepts are not limited thereto. As will be described below inconjunction with FIG. 7 , one of the 12 first wafers, one of the 12second wafers, and one of the 12 third wafers, will be selected andcombined. Such combinations of selected wafers correspond to each row ofthe tables in FIGS. 6A and 6B.

As illustrated in FIG. 6A, one total combination is provided by 12combinations C1 through C12 using the first, second, and third wafers210, 310, and 410. Each yield (Yd; Y1 through Y12) for the combinationsC1 through C12 may be calculated based on whether each location of eachwafer is defective or not, which was determined previously, and a totalcombination yield Yt1 may be calculated by summing these yields.

More specifically, each individual wafer has one or more locations to bemeasured for the performance. After the measurement, it is determinedwhich locations are defective or which locations are not defective. Theinformation for the defective locations on each individual wafer issufficient for calculating the combination yield as will be furtherdescribed below. Here, the “yield” means a percentage (%) ratio of goodlocations to a total locations. The yield of each individual wafer canbe determined based on the measurement results, but the yield of theindividual wafer may not be used for calculating the combination yield.

By way of example, calculation for a combination yield C1 for thecombination of R1, B1, and G1 wafers is described. For convenience ofexplanation, it is assumed that there are hundred (100) locations foreach individual wafer, and ten (10) defective locations for eachindividual wafer. The combination yield depends on how many overlapsamong the defective locations on each individual wafer in thecombination are. More specifically, by way of example only, if ten (10)defective locations of the R1 wafer, ten (10) defective locations of B1wafer, and ten (10) defective locations of G1 wafers overlap alltogether, a combination yield of the combination of R1, B1, and G1wafers is 90%. That is, the combination yield of the combination of R1,B1, and G1 equals to 100*(100−10)/100. If there is no overlap betweenthe defective locations of the R1, B1, and G1 wafers, then there will be30 defective locations for the combination of the R1, B1, and G1 wafers.Thus, the combination yield will be 70% based on the calculation of100*(100−30)/100. Therefore, as described above, the combination yieldcan be calculated based on the information of the defective locationsfor the three wafers.

The total combination yield Yt1 is a total combination yield obtainedwhen the first, second, and third wafers 210, 310, and 410 are combinedin the combination C1 through C12 as illustrated in FIG. 6A. Meanwhile,when they are combined differently from FIG. 6A, the yield Yd for eachcombination may be changed, and thus, the total combination yield Ytwill also be changed. For example, as illustrated in FIG. 6B, even whenonly an order of the second wafers 310 is changed, combinationscompletely different from those of FIG. 6A are formed, and accordingly,a new total combination yield Yt2 is calculated.

When the number of the first wafers 210, the second wafers 310, and thethird wafers 410 is n, respectively, possible combinations may be (n!)²combinations. More particularly, by way of example, when the number ofthe first, second, and third wafers 210, 310, and 410 is 12,respectively, total combination yields of (12!)² can be calculated.Among these total combination yields of (12!)², 12 combinations C1through C12 representing the maximum combination yield can be determinedand selected. The maximum combination yield is the maximum combinationyield that can be obtained by combining the first, second, and thirdwafers 210, 310, and 410 in the first group in one or more certainorders, and yields of light emitting devices may be maximized bycarrying out a subsequent process with these combinations.

In other embodiments, each number of the first wafers 210, the secondwafers 310, and the third wafers 410 may be different. One of the firstwafers 210, the second wafers 310, and the third wafers 410 are selectedand combined to make a stacked structure. When the first, second andthird wafers have different numbers, the total combination should bemade with a same number of wafers. For example, there are ten (10) firstwafers, fifteen (15) second wafers, and twenty (20) third wafers, theircombination yields will be calculated from 10 first wafers, 10 secondwafers selected from the 15 second wafers, and 10 third wafers selectedfrom the 20 third wafers. In addition, all combinations of the first,second, and third wafers 210, 310 and 410 may be considered such thatthe combination yields of all combinations of the wafers 210, 310 and410 can be calculated with respect to the 10 first wafers, 15 secondwafers, and 20 third wafers. In other words, with respect to the 10first wafers, all of 15 second wafers and all of 20 third wafers will beconsidered to make different combinations and for each differentcombination, the combination yield will be calculated.

In some forms, the calculation of the above combination yields may beperformed using a computational program. The computational program maycalculate the yield of each combination by performing an operation basedon the measurement result of each of the first, second, and third wafers210, 310, and 410. The computational program may be performed using anoperation device such as a computer system, and the operation may beperformed based on the measurement result for each wafer. Thecomputational program may be stored in a computer-readable recordingmedium.

In another exemplary embodiment, another method may be considered inaddition to the method of considering all possible combinations asdescribed above. For example, to reduce the number of cases, an order ofone type of wafers may be fixed, and combinations of the remainingwafers may be considered. In some forms, the order of the first wafersis fixed and total combination numbers are determined by the combinationof the second wafers and the third wafers.

For example, the first wafers R1 through R12 may be arranged in order ofhigh yield, and a combination having a highest yield may be derived inthis order. More particularly, first, combination yields Y1 through Y12are calculated for all combinations of the first wafer R1 having thehighest yield among the first wafers R1 through R12 with the secondwafers B1 through B12 and the third wafers G1 through G12, and acombination with a highest combination yield Y1 among them isdetermined. When a combination selection for the first wafer R1 iscompleted, a combination representing an optimum yield Y2 for the firstwafer R2 is determined through the same manner with the second wafersand third wafers except for the second wafer and the third wafercombined with the first wafer R1. In this way, all combinations C1through C12 representing the yields from the highest yield Y1 to alowest yield Y12 may be determined. According to this method, the numberof combinations for which the yields are to be calculated may besignificantly reduced compared to that of the previous case.

Although the first wafers R1 through R12 are described above as beingfixed in advance in order of high yield, the second wafers B1 throughB12 may be fixed in advance in order of high yield, or the third wafersG1 through G12 may be fixed in advance in order of high yield. Inparticular, the order of wafers having relatively high yields among thefirst, second, and third wafers 210, 310, and 410 may be fixed inadvance.

(Step 401)

In Step 401, combinations of wafers on which the process is to beperformed are determined based on the calculation of the combinationyields of the first, second, and third wafers 210, 310, and 410 in thefirst group. In an exemplary embodiment, the combinations of wafers onwhich the process is to be performed may be determined with a totalcombination of C1 through C12 representing a maximum combination yieldYt among all possible combinations. In another exemplary embodiment, thewafer combinations on which the process is to be performed may bedetermined with all combinations in which the order of the first wafersR1 through R12 is fixed in advance and individual combination yields Ydare arranged in order of high yield according to this order.

(Step 501)

In Step 501, the process is carried out according to the determinedcombinations of wafers to fabricate light emitting devices. Theprocesses may include forming an electrode on each wafer, and may alsoinclude bonding the wafers 210, 310, and 410 to one another.Furthermore, after the wafers are bonded to one another, at least one ofthe substrates 21, 31, and 41 may be removed.

Fabricating light emitting devices using the first, second, and thirdwafers 210, 310, and 410 may be performed in various ways using knowntechniques.

FIG. 7 is a schematic perspective view illustrating a method offabricating a light emitting device having a stacked structure accordingto an exemplary embodiment.

Referring to FIG. 7 , a first wafer 210 may generally include at leastone defective location 23 f. A second wafer 310 and a third wafer 410may also include defective locations 33 f and 43 f, respectively.

According to the method of fabricating a light emitting device accordingto an exemplary embodiment, combinations of wafers in which thedefective locations 23 f, 33 f, and 43 f of the first wafer 210, thesecond wafer 310, and the third wafer 410 are arranged at an identicallocation may be selected. As shown in FIG. 7 at least one of thedefective locations of each wafer is set to be overlapped with thedefective location of another wafer, and a manufacturing yield of thelight emitting device may be improved compared to combinations of wafersin which the defective locations thereof are not overlapped.

Meanwhile, although it is illustrated that the second wafer 310 isdisposed on the first wafer 210, and the third wafer 410 is disposedthereon, the inventive concepts are not limited thereto. For example,the second wafer 310 may be disposed on the third wafer 410, and thefirst wafer 210 may be disposed thereon.

In addition, when the wafers are bonded, the present disclosure is notlimited to all substrates 21, 31, and 41 disposed below as illustratedin FIG. 7 . For example, when the second wafer 310 is bonded onto thefirst wafer 210, the substrate 31 of the second wafer 310 may bedisposed opposite to the first wafer 210. After the second wafer 310 isbonded onto the first wafer 210, the substrate 31 may be removed using alaser lift-off technique, for example. In this case, a correspondingmeasurement location of the second wafer 310 with respect to eachmeasurement location of the first wafer 410 is opposite to that in thecase where the substrate 31 faces the first wafer 210. Therefore,considering the wafer bonding method in the process, the yields of thecombinations of wafers need to be calculated.

Meanwhile, although the process may be performed on the combinations ofall the wafers 210, 310, and 410 in the first group, all the wafers maynot be used in fabricating light emitting devices. For example, wafersof a combination in which a combination yield Yd is less than or equalto a reference value may be held or discarded. The reference value maybe set to be 50%, further, 60%, or 70%, for example.

Meanwhile, discarding all of the wafer combinations in the first groupeach having a combination yield less than the reference value may causelosses. For example, there might be a case that a yield of one wafer maybe very low and yields of other wafers may be relatively favorable, orthere might be a case that, even though a yield of each of wafers isrelatively favorable, a combination yield of the wafers may berelatively low because defective locations are not overlapped with oneanother. In this case, when the process is performed using the wafers ofthese combinations, the yield of the light emitting devices is poor,resulting in a greater process loss. Hereinafter, a method of utilizingthe wafers in the first group will be described.

FIG. 8 is a schematic flowchart illustrating a method of fabricating alight emitting device having a stacked structure according to anexemplary embodiment. Herein, the method of fabricating a light emittingdevice will be described together with the flow chart described withreference to FIG. 2 .

(Step 103)

In Step 103, a second group of wafers is prepared. The second group ofwafers include first wafers 210, second wafers 310, and third wafers 410as the first group of wafers. However, the second group of wafers arewafers that do not belong to the first group and are distinguished fromthe first group of wafers. For example, the second group of wafers maybe prepared through a different run from that for the first group ofwafers.

The numbers of the first wafers 210, the second wafers 310, and thethird wafers 410 included in the second group are not particularlylimited. In addition, the first, the second, and the third wafers 210,310, and 410 may be prepared in an identical number to one another, butmay be prepared in different numbers from one another.

(Step 203)

In Step 203, a performance measurement for each wafer in the secondgroup is carried out. The performance measurement for locations in eachwafer is carried out, and whether there is a defect at each location ornot may be determined using the measured value. As previously describedwith reference to FIGS. 3, 4 and 5 , it is checked whether or not eachof regions 23 m, 33 m, and 43 m of the first, second, and third LEDstacks 23, 33, and 43 grown on the first, second, and third wafers 210,310, and 410 is defective, and the result of checking of whether eachlocation is defective or not, may be stored. The defect and thecorresponding location are mapped so that it can be checked visually.

In Step 203, the performance measurement of all the wafers in the secondgroup is completed, and whether each location of each wafer is defectiveor not is determined. According to the above results, a yield of eachwafer may also be extracted.

(Step 303)

In Step 303, wafer combination yields are calculated by mixing a portionof first group of wafers and the second group of wafers. For example, asdescribed above, at least a portion of first group of wafers among thewafer combinations of the first group having combination yields lessthan the reference value may be merged into the wafers of second group,and total combination yields thereof may be calculated. As describedabove, the combination yields may be obtained by calculating the totalcombination yields for all combinations of all wafers, or by fixing anorder of any one of the first, second, and third wafers 210, 310, 410 inadvance and calculating an optimum yield of each combination.

(Step 403)

In Step 403, a total combination of wafers consisting of the portion offirst group of wafers and the second group of wafers is determined basedon the previously calculated yields. As such, the wafers may be combinedsuch that the total combination of wafers may achieve the optimum yield.

(Step 503)

In Step 503, the process is carried out according to the determinedcombinations of wafers to fabricate light emitting devices. Since theprocess of fabricating light emitting devices for the combinations ofwafers is the same as described above, detailed descriptions thereofwill be omitted. In addition, it is not required to carry out theprocess of fabricating light emitting devices for all combinationsincluding all or a portion of first group of wafers, all or a portion ofthe second group of wafers, or both, but some of these wafers may bediscarded, or merged with wafers of other groups.

According to the illustrated exemplary embodiment, the wafers eachhaving a relatively low combination yield among the wafers in the firstgroup are merged with the wafers in the second group, and it is possibleto reduce wafer loss by reducing discarded wafers and improving theyield.

Meanwhile, in various exemplary embodiments, individual combinationyields Yd and total combination yields Yt according to variouscombinations of the first wafers R1 through R12, the second wafers B1through B12, and the third wafers G1 through G12 included in the firstgroup may be calculated using a computational program. Thiscomputational program calculates a yield according to a combination ofthe first, second, and third wafers 210, 310, and 410 based on ameasurement value at each location of the wafer or based on adetermination as to whether there is a defect according to themeasurement value. For example, the combination yields of R1, B1, and G1in which the first wafer R1, the second wafer B1, and the third wafer G1are combined represent percentage of the number of measurement locationswhere favorable measurement locations in all 3 wafers overlap when thethree wafers are bonded, with respect to the total number of measurementlocations in one wafer. The computational program may calculate thecombination yields using the data on the stored measurement location,calculate the combination yields for all possible combinations, andcalculate the total combination yields Yt accordingly.

By using the computational program, the calculation of the combinationyields may be carried out quickly, and thus, the process time dependingon the process of calculating the combination yields may be reduced.Furthermore, as described above, the number of combinations calculatedmay be reduced by fixing the orders of the group of first wafers RG, thegroup of second wafers BG, or the group of third wafers GG in advance.

The computational program may be integrated into a computer system toperform the procedure for calculating the combination yields. Typically,the computer system may include a central processing unit (CPU), memory,and input/output interfaces. The computer system may be aspecial-purpose computer system or a general-purpose computer system.

The computer system is generally coupled with an output apparatus suchas a display or various input apparatuses such as mouses and keyboardsthrough I/O interfaces. In addition, the computer system may includevarious circuits such as cache, power supplies, clock circuits, and acommunication bus.

The display may aid a user's visual understanding by displaying themeasurement result of each wafer or the combination yields according tothe combinations of wafers, for example, in a wafer map.

A memory 420 may include a random access memory (RAM), a read onlymemory (ROM), a disk drive, a tape drive, or a combination thereof.

The computational program may be stored in an internal or externalmemory, or may be stored in the computer as software, and may beexecuted by the CPU.

The light emitting device described herein may be a display apparatuscalled a micro LED or a mini LED. The light emitting device may be usedin a large display apparatus such as an LED TV, a VR display apparatussuch as a smart watch 1000 a, a VR headset 1000 b, or an AR displayapparatus such as augmented reality glasses 1000 c.

Although some embodiments have been described herein, it should beunderstood that these embodiments are provided for illustration only andare not to be construed in any way as limiting the present disclosure.It should be understood that features or components of an exemplaryembodiment can also be applied to other embodiments without departingfrom the spirit and scope of the present disclosure.

The invention claimed is:
 1. A method of fabricating a light emittingdevice having a stacked structure, comprising: measuring an emissionwavelength for each predetermined measurement location of each wafer afirst group of wafers, wherein the first group of wafers comprises aplurality of first wafers, a plurality of second wafers, and a pluralityof third wafers, and a set of wafers comprises at least one of the firstwafers, at least one of the second wafers, and at least one of the thirdwafers; determining whether each measurement location is defective ornot based on a measurement result of the emission wavelength of eachlocation; forming a test stacked structure by combining said one of thefirst wafers, said one of the second wafers, and said one of the thirdwafers; calculating a combination yield of the test stacked structurebased on a count of defective measurement locations that overlap in thetest stacked structure; selecting one or more resultant combinations ofthe first, the second and the third wafers by comparing each combinationyield of the test stacked structure; and performing a subsequent processusing the resultant combinations of the first, the second and the thirdwafers, wherein the subsequent process comprises forming a final stackedstructure with the selected resultant combinations of first, the secondand the third wafers.
 2. The method of fabricating a light emittingdevice of claim 1, wherein: performing the subsequent process furthercomprises performing the subsequent process on the combinations offirst, the second and the third wafers, where each combination has acombination yield greater than or equal to a reference value.
 3. Themethod of fabricating a light emitting device of claim 1, furthercomprising: determining each yield of each wafer in the first groupbased on the measurement result of the emission wavelength of eachlocation.
 4. The method of fabricating a light emitting device of claim1, wherein determining whether each location is defective or not furthercomprises determining whether or not the measurement result of theemission wavelength of each location is in a preset range from a targetwavelength.
 5. The method of fabricating a light emitting device ofclaim 1, wherein measuring the emission wavelength further comprisesmeasuring the emission wavelength using photoluminescence.
 6. The methodof fabricating a light emitting device of claim 1, further comprising:sorting the plurality of first wafers to follow a selected order;wherein forming the test stacked structure further comprises forming thetest stacked structure by combining each first wafer following thesorted order with each second wafer and each third wafer selected inrandom order, respectively.
 7. The method of fabricating the lightemitting device of claim 1, wherein each first wafer having a firstsubstrate and a first LED stack grown on the first substrate; eachsecond wafer having a second substrate and a second LED stack grown onthe second substrate; and each third wafer having a third substrate anda third LED stack grown on the third substrate, wherein the first,second, and third LED stacks are configured to emit light of differentcolors from one another.
 8. The method of fabricating the light emittingdevice of claim 7, wherein: the first LED stack is configured to emitred light, the second LED stack is configured to emit blue light, thethird LED stack is configured to emit green light, and the second LEDstack is disposed between the first LED stack and the third LED stack.9. The method of fabricating the light emitting device of claim 7,wherein: the first LED stack is configured to emit red light, the secondLED stack is configured to emit green light, the third LED stack isconfigured to emit blue light, and the second LED stack is disposedbetween the first LED stack and the third LED stack.
 10. The method offabricating the light emitting device of claim 1, further comprising:preparing the first group of wafers including a total of n first wafers,a total of m second wafers, and a total of k third wafers, wherein n, mand k are natural numbers greater than zero.
 11. The method offabricating the light emitting device of claim 10, wherein: where m andk are equal to n, forming the test stacked structure further comprisesforming the test stacked structure that include (n!)² differentcombinations of the first wafers, the second wafers, and the thirdwafers.
 12. The method of fabricating the light emitting device of claim11, wherein: calculating the combination yield of the test stackedstructure further comprises calculating the combination yield of all ora part of the (n!)² different combinations based on the count ofdefective measurement locations that overlap in each test stackedstructure.
 13. The method of fabricating the light emitting device ofclaim 12, wherein: selecting the resultant combinations furthercomprises comparing the combination yield for all or a part of the (n!)²different combinations of the first wafers, the second wafers, and thethird wafers.
 14. The method of fabricating the light emitting device ofclaim 12, further comprising: calculating total combination yield Yt bysumming the combination yield of all of a part of the (n!)² differentcombinations of the first wafers, the second wafers, and the thirdwafers.
 15. The method of fabricating a light emitting device of claim1, wherein: selecting the resultant combinations further comprisesselecting the resultant combinations of the first, the second and thethird wafers in the order of a highest combination yield.
 16. The methodof fabricating a light emitting device of claim 10, further comprising:where m is greater than n: selecting n sets of wafers from the firstgroup of wafers; calculating the combination yield of the test stackedstructure based on the n sets of wafers; selecting (m−n) sets of wafersfrom the first group of wafers; and calculating the combination yield ofthe test stacked structure based on the (m−n) sets of wafers.
 17. Themethod of fabricating a light emitting device of claim 1, comprising:preparing a second group of wafers including wafers of identical typesto types of the first group of wafers; measuring the emission wavelengthfor each predetermined measurement location of each wafer in the secondgroup of wafers; forming another test stacked structure by combining aportion of the wafers in the first group and the wafers in the secondgroup; and calculating combination yields of another test stackedstructure based on a count of defective measurement locations thatoverlap in another test stacked structure.